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Perhaps tracing back to after-school TV specials or teen magazines, many Americans still envision “serious” eating disorder cases as stick-thin and sad-eyed—in other words, obvious. Sometimes this stereotype proves to be true, but more often, it doesn’t. The mental illness, like its victims, comes in all shapes and sizes. Underneath a robust exterior can lurk, quite literally, flesh-eating demons.

For Margo Peterson, a telling comment came on a trip to an Oregon emergency room last December. She'd burst a blood vessel in her throat while throwing up. The on-call physician, someone she knew and liked, mistook her athletic physique for health, commenting: You don't look like you have a problem.

“It was frustrating,” she told The Daily Beast.

A recovering anorexic, Peterson, 27, had stopped starving herself, but had begun throwing up her food to compensate. Because she didn’t always binge first, she wasn’t technically bulimic. Instead, a doctor gave her the DSM-IV diagnosis of “Eating Disorder Not Otherwise Specified,” or EDNOS. (The DSM, or Diagnostic and Statistical Manual of Mental Disorders, is the bible of mental illnesses published by the American Psychiatric Association.)

What most people don’t realize about eating disorders is that of the nearly 10 million Americans who suffer from these conditions, more than 60 percent are diagnosed with EDNOS. The catch-all category includes many patients who fall just one or two criteria short of anorexia nervosa or bulimia nervosa: They haven’t stopped menstruating for three months in a row, for example, as required of an anorexia diagnosis. Or they binge and purge once a week, instead of twice, as “official” bulimics do. Because of the vague label, many clinicians, parents, insurance companies, and even patients assume they’re not as sick as “real” anorexics or bulimics.

Yet a breakthrough new study reveals that many with EDNOS suffer from medical complications just as severe as those with an anorexia or bulimia diagnosis—sometimes worse. Patients’ heart rates, blood pressure, temperatures, and electrolyte counts, as well as damage to internal organs were often comparable, the Pediatrics report found. More than half of those with EDNOS met the medical criteria for hospitalization. Perhaps more troubling, many EDNOS patients aren’t getting the treatment they need, author Dr. Rebecka Peebles, who specializes in pediatric and adolescent eating disorders at Stanford University, told The Daily Beast.

“EDNOS is such a vast term, people often don’t know what to do with it,” Peebles said. “If parents hear that their child doesn’t meet criteria for anorexia or bulimia yet, they’re relieved”—often when they shouldn’t be.

A committee is now at work revising the section on eating disorders in the next edition of the DSM, set to publish in 2013. According to task force leader Dr. Tim Walsh, the group is sensitive to the issues EDNOS presents, and they’ve broadened descriptions for anorexia and bulimia. They’ve also suggested a new diagnosis: Binge eating disorder, in which victims binge but don’t purge. Until now, it’s fallen under EDNOS.

But the EDNOS diagnosis is vast. Along with shades of anorexia and bulimia, it encompasses several little-known, emerging disorders—illnesses that haven’t been studied enough to acquire their own diagnosis, but that might in the future. The Daily Beast looks at five of these “secret” yet serious disorders.

1. Orthorexia

While the rise of Whole Foods and the organic movement is inspiring many Americans to eat healthier, it’s also encouraging a controversial new eating disorder. People with orthorexia compulsively avoid foods thought to be unhealthy or unnatural—including foods with trans fats, artificial colors or flavors, high-fructose corn syrup, and preservatives. Many opt instead for strict vegan or raw foods diets. They’ll choose to eat nothing over something processed—and as a result, often end up malnourished and excessively thin.

In this way, the disorder closely resembles anorexia. “Patients with eating disorders search for ways to rationalize their disorder,” Dr. Angela Guarda, director of Johns Hopkins eating disorders program, told The Daily Beast. “Orthorexia is kind of fashionable, it sounds good. [For some], it’s a way to kind of explain their behavior that is more culturally acceptable.”

2. Chewing and Spitting

By nature, eating disorders are secretive—but some habits are particularly alienating. Chewing and spitting falls into this category. While Glamour magazine dubbed it a “scary new eating disorder” in 2008, it rarely manifests as a standalone problem, usually surfacing in conjunction with other behaviors.

People who chew and spit take bites of food—usually foods high in sugar, salt, and fat—chew it, then (as the name suggests) spit it out into a cup or napkin. They keep the food in their mouth long enough to activate the brain’s pleasure sensors, but don’t absorb its calories or nutrients. Over time, these patients develop visibly enlarged salivary glands; they can also become malnourished. “It’s a behavior that patients rarely volunteer,” said Guarda. “Some, a minority, do it as their primary method of purging. Most just do it on occasion, or in small amounts.” Those who chew and spit regularly can become nearly addicted to the process.

3. Night Eating Syndrome

Many people eat a late-night snack every now and then, but when does night eating become a mental illness? When patients obsessively consume at least a quarter of their daily intake after dinner, or when they wake up in the middle of the night to eat at least twice a week, experts say. As many as 6 million people suffer from Night Eating Syndrome, including about 9 percent of extremely obese individuals. Those afflicted report feeling a loss of control and significant distress. Because their sleep is interrupted, they also report difficulty concentrating during the day. And emerging studies suggest eating in this way may affect hormones, leading to diabetes and metabolic syndrome.

“Doctors don’t know much about Night Eating Syndrome, or how to treat it,” Dr. Kelly Allison, assistant professor of psychology at the University of Pennsylvania School of Medicine and an expert in the disorder, told The Daily Beast. “I’m hopeful that even being listed under EDNOS [in the DSM-V] will make it more of a valid disorder.”

4. Purging disorder

Contrary to popular belief, not all purges follow binges: Those with purging disorder make themselves throw up or use laxatives after eating even small amounts. This disorder can wreak havoc on patients’ digestive systems, as well as on their heart and kidney function. Many in this category also develop an addiction to laxatives, taking industrial amounts every day to achieve the desired result. When they try to wean themselves off the pills, they find it nearly impossible, at first, to go to the bathroom normally.

Before 2007, this disorder was rarely recognized or researched. That year, Dr. Pamela Keel, a psychologist at Florida State University and leading expert on purging disorder, published a breakthrough paper on the topic. She says she received an influx of emails after the study was published: “Some people were unsure if they really had an eating disorder,” Keel told The Daily Beast. “People would describe being worried about themselves, internally—but didn’t think they had a ‘real’ or ‘full’ eating disorder.”

People also expressed frustration in seeking treatment: “Clinicians would treat them as if they had bulimia nervosa," she said. "They’d try to reduce frequency of binge episodes, which they didn’t have."

5. Binge eating disorder

When the DSM-IV was published in 1994, binge eating disorder was listed in the manual’s appendix as a condition warranting further research. At that time, around two-dozen studies existed on the topic. Since then, it’s become the focus of nearly 1,000 reports. “[Including it] provided a stimulus for hundreds of articles that were written in last several years,” says task force leader Walsh. In the DSM-V, committee members recommend that it be listed as its own diagnosis.

With binge eating disorder, the millions afflicted binge, but don’t purge afterward. The disorder primarily affects people who are overweight, but people at healthy weights suffer from it, too. Victims report regularly eating large quantities of food while feeling out of control. They also report significant distress from the condition. Some will restrict their eating following a binge, others won’t. By separating it from EDNOS, these millions will have a better shot at receiving the treatment they need.

Danielle Friedman has worked as a nonfiction book editor for Hudson Street Press and Plume, two imprints of Penguin Group. Her writing has been published in the Miami Herald, the Seattle Post-Intelligencer and on CNN.com. She is a graduate of the Columbia University Graduate School of Journalism.